As described in published German Patent Application No. 3,610,557, a known problem in winding webs of paper onto a rigid core is that the adhesive tape used to secure the leading edge of the web to the core will cause an embossing of the paper for many turns of the web on the core. This embossing occurs by virtue of the finite thickness of the adhesive tape, and the high radial pressure which builds up as successive turns are wound on the core. The leading edge of the web also causes such embossings. Web containing such embossings is generally useless and has to be discarded.
As described in published German Patent Application No. 3,610,557, a solution to the problem is to provide the core with a coating of elastically or plastically deformable material which deforms to accommodate the irregularity. As such, the web of the first turns on the core does not deform to accommodate the irregularity.
When manufacturing webs, particularly webs of base material for photographic film, problems arise from the lack of uniformity in thickness (often referred to as "gage") across the web. One such problem arising from gage non-uniformity is known as gage bands. Gage bands occur, for example, when a region of increased thickness is at a lateral constant position. Then, as the web is wound on a core, the increased thickness regions of each turn will lie on top of the increased region of the previous turn. With gage bands, very high localized pressure often results in undesirable effects, such as abrasions, deformations, chemical changes, and physical changes. A known solution to gage bands is to make the margins thicker, or to knurl the margins of the web so that the protuberances produced by the knurling are higher than any gage increase likely to be encountered during normal manufacturing. Thus, when the web with the knurls along its two margins is wound on a conventional rigid core (with a non-deformable surface), the knurls in the margins wind on top of themselves. It is in these areas, rather than where the gage increases overlap one another, that the areas of high pressure are encountered. During manufacture, the margins containing the knurls are slit off and discarded, while the entire portion of the web between the knurls is assumed to be free from defects attributable to gage bands.
It has been noted that when a web having knurled margins is wound onto a deformable core, such as described in published German Patent Application No. 3,610,557, if the deformable coating is soft enough to avoid undesirable embossings caused by the securing tape or leading edge, the very high pressures progressively created by the overlapping knurls cause the wound web to collapse radially inwards. Such collapses are not localized, and extend along the roll axially from the edges of the web toward the middle of the width of the roll. Permanent damage to the web occurs from the collapse, requiring an increased width of the web at the margins to be slit off and discarded, resulting in undesirable increased waste and correspondingly lower productivity.
U.S. Pat. No. 4,934,622, assigned to same assignee, incorporated herein by reference, describes a means for avoiding embossing and collapse of the wound roll. A first resilient sleeve is supported on a rigid member. A second and third sleeve, harder than the first sleeve, are positioned contiguous with the ends of the first sleeve, and are intended to underlie the margins of the web.
While the above-identified apparatuses has achieved a certain degree of success, impressions can be created from the sharp transitions between the sleeves, and one particular core cannot accommodate webs of varying widths. For example, if a narrower web were wound onto the core, the knurls would be positioned over the first sleeve, causing the roll to collapse. Alternately, if a wider web were wound onto the core, the impression from the sharp transition would occur within the non-knurled, (i.e., saleable) portion of the web.
The present invention provides a modular design, thereby assisting in the reduction of manufacturing costs by allowing the modular components to be recycled or readily replaced. Further, a gradual transition zone allows a particular core size to accommodate webs of varying widths.
Accordingly, a need exists for a core for winding a web of deformable material which accommodates various web widths, is not complex, can be manufactured inexpensively, affords modularity, avoids embossing, and is able to avoid collapse.